This invention relates to a hydraulic calcium phosphate cement composition and a cement composition containing a hardening liquid which are usable as a filler for filling in a defect or hollow portion of bone or a dental root canal portion.
It has been known that a hydraulic calcium phosphate cement composition is useful as a repairing material for teeth and bones of a living body since the calcium phosphate cement composition is converted into compounds resembling main ingredients of teeth and bones due to setting and hardening and is also useful as an absorbing agent for living tissue polymers and for organic substances or inorganic ions harmful in the living body.
In Japanese Laid-open Patent Application No. 59-88351, a hydraulic calcium phosphate cement composition using a hardening liquid containing salts and dilute acids in combination is disclosed. Further, in Japanese Laid-open Patent Application No. 60-253454, a calcium phosphate cement composition using an acid solution containing an unsaturated carboxylic acid polymer is disclosed.
However, the conventional hydraulic calcium phosphate cement compositions have disadvantages that living body is considerably stimulated as the hardening liquid has a strong acidity until the hardening of the cements are completed. Further, even after the cement composition is hardened using the hardening liquid, the unreacted acid is eluted into the living body fluid to thus lower pH value, resulting in stimulating the living body.
To solve these problems, therefore, a hydraulic calcium phosphate cement composition hardenable with water is developed (for example, "FC REPORT", vol. 6 (1988), pp. 475.about.480 "Hydraulic Apatite as Bioceramics"). More in detail, proposed by Japanese Laid-open Patent Application No. 64-37445 is a hydraulic calcium phosphate cement composition hardenable by mixing and kneading with only water at 37.degree. C. for about 10 minutes. Since this cement composition has almost neutral pH value, such composition has less stimulation to the living body, thus eliminating the disadvantages associated with the conventional hydraulic calcium phosphate compositions.
However, this cement composition has another problem that there is extremely high risk of deterioration and degradation in the living body since the cement composition contains .alpha.-type calcium tertiary phosphate and calcium secondary phosphate dihydrate with a molar ratio of Ca/P of 1.20 to 1.47 so that when the cement composition is left in water for a long time, it is extremely degraded, leading to destruction in the living body.